Pneumatic control instrument



Oct. 7,1941. I sHlVERS 2,258,559

PNEUMATI C CONTROL INSTRUMENT Filed Dec. 31, 1937 2 Sheets-Sheet 1 P m 0 cl 4: u' w 0 "8 v a N Oct. 7, 1941. P. F. SHIVERS PNEUMATIC CONTROL INSTRUMENT Filed Dec. 31, 1957 2 Sheets-Sheet 2 TO OTHER TH ERMOS TATE Patented Oct. 7, 1941 PNEUMATIC CONTROL INSTRUMENT Paul F. Shivers, Wabash, Ind., assignor to Minneapolis-Honey-well Regulator Company, Minneapolis, Minn., a corporation" of Delaware Application December 31, 1937,.Serial No. 182,787

Claims.-

The present invention relates topneumatic control apparatus and is more particularly con-- cerned with an improved compressed air then-- mostat and pneumatic relay device forproviding more effective and efficient control of the temperature in the rooms of a building during the daytime and at night.

In school houses or other buildings,. it is a. matter of fuel economy to maintain lower temperatures at night when the building may be unoccupied. Inthe present invention, thermostats may be employed to control steam. valves in various rooms of a building and may be reset to maintain lower temperatures at night by changing the operating pressure in the pneumatic system at a remote point. Pneumatic. relay devices are often employed with air op.- erated control instruments for multiplying, the capacity of the instrument whereby larger valves or other devices may be controlled. My invention employs a. relay ofimproved construction such that while the operating pressure in the pneumatic system may be changed. for resetting the thermostats, the pressure which can be. transmitted by the relay to valves. damper mirtors, or the like, cannot exceed a predetermined. value. Such automatic. valves. or damper: motors.- are usually designedfor complete closure. at'a;

predetermined pressure; and: my invention designed to prevent a. higher. pressure: from being impressed upon them. with consequent: danger of harmful and damaging result'a.

Frequently in school buildings; or. thelikeLthe-i janitor may reset the. thermostats. in all. the. rooms of the building from aremote point, for example from the basement, at ascertain time in the evening. Often it may be desired: tomain'w tain certain rooms at the. daytime temperaturev after that time to accommodate people using the rooms later than usual.- My improved thermostat is so constructed. thatit maybesre set to a nightsetting from a remote. point and also can be manually returned to the day sets ting and back tothe night setting as desired so that individual rooms may be. kept warm as long as necessary without-supplying;heat to theentire building. The instrument is also so arranged that it. can be accuratelyadjusted in either'the day or night position. to maintain a desired temperature.

In my invention the normaldaytime pressure. cmployedin the pneumatic controlsystemis-r 151 lbs. while at night this. pressure. is increased-to. 30. lbs. for accomplishing theresetting. operaillustrating the. position of. the parts-shown when. the; instrument has been manually returned to V i the-.daytimesetting'after: having been reset to 'tion. of..thc control. instruments; These: presisures may, of course, be varied within the contemplation and scope of the invention.

It is an object of my invention to provide a.

Another object of my invention is to providea. novel pneumatic temperature responsive control instrument, the control point of which can be reset from a remote point by changing. the supply pressure in the pneumatic system and which has-a device:incorporated therein for returning, thecontrol point to the daytime setting at-will after it has been reset to a night-time setting.

It is afurther object of the invention to provide. improved pneumatic control apparatus. for heating: systems and thelike whereby more;flex:-

ible control may be exercised over the system and more'eflicient and economical operation will. result.

Further objects and advantages of the invention will make themselves apparent to those. skilled in the art from the following detailed description of the. invention and: accompanying drawings thereof.

Figure- 1 is a perspective viewof my complete assembled control instrument exclusive of its casing.

Figure 2 is a side View of the instrument of Figure 1, havingcertainportions shown in cross section, illustrating the arrangement of the parts when theinstrument is' on the normal daytime setting.

Figure 3 ma side view similar to Figure 2. but illustrating the position of the instrument is on the night setting.

Figure. 4 is aside view of a detail portion of theinstrument as. seen on Figures Z-and 3 but the night? setting:

parts; when th & HUNHUHY Hl-MULAHUIJ. @033 lielci't'lltfi Search Room Figure 5 is a side elevation in cross-section of the improved pneumatic relay forming part of my control instrument taken along the line 5-5 of Figure 1.

Figure 6 is a more or less diagrammatic illustration'of a complete pneumatic control system having some of the elements thereof in section and showing the manner of interconnecting the parts of my control instrument with the system; and the operative relationship therebetween.

Figure 7 is a side elevation partly in cross-section of a slightly modified form of the pneumatic relay of Figure 5.

Referring to Figures 1, 2 and 3 of the drawings which represent my control instrumentin assen bled form, numeral I indicates the body-or frame of the instrument. The body I has apair of op,- positely arranged lugs, one of which is visible at 2, which are arranged for attachment of the body to a pipe head 3 by means of screws 4. The pipe head 3 is a cast metal plate having connections for a pair ofpipes 50 and 6, one of which provides for communicating a constant pressure to channel 5a and to the instrument and the other of which provides for conveying a pressure regulatedby the instrument from channel 6a to a device such as a valve or damper motor to be controlled. Interposedbetween the body I of the instrument and the pipe head 3 is a gasket 9 for providing a leak-proof joint between the-body I and the pipe head 3.

The body I has a pair ofarms I and II extending therefrom which are perforated at their ends to receive a shaft I2. Pivoted-on the shaft- I2 are a bell-crank lever I- and a lever I6. The lever I6 has a pair of lugs or ears I'I- through which the shaft I2 extends. Connected to the lower part of lever I6 by riveting or-byothersuitable means is one leg of a U-shaped member 20. The opposite leg of the U-shaped member is shorter and has attached thereto by riveting, or the like, a thermostatic or bimetallic element 2|. Ilhe bell-crank lever I5 has a pair of integral ears or lugs similar to the lugs ll' of' lever I6 and through which also extends the shaft I2. The downwardly extending part of the bell-crank lever I5 is forked, forming a pair of arms- 22- which are integrally formed with the lugs engaging the shaft I2. The arms 22'engage with the surface of a diaphragm 23 on the movable end of a bellows 24 which is mounted on the body I of the instrument. also carries a member 25 which engages the lever arm I6 as shown. The bell-crank lever I5 also has a portion 21 which extends generally at right angles to the arms 22. A branch channel'5b communicates pressure from pipe 50 to bellows 24.

The body I of the instrument is broader atits central portion and has extending members which are tapped to receive the screws 3|. The screws 3! extend through the opposite ends of a yoke 32 which is spaced from the body I of the instrument by coil springs 33. Numeral 35 indicates a member in screw threaded relation withtheh central porttion of the yoke 32 and rotatable by means of a knurled knob, or the like, 36. The end of the screw member 35 serves as a stop for the lever I6 when the said lever is moved tothe right as seen on the figures and which is adjustable by turning the knurled knob 36 to-the right or left. The assembly formed by the levermember I6 and the U-shaped member- 2Il is resiliently engaged between the member 25 at the end of the bellows 2.4. and betweena forkedresilient metal spring 40. The forked spring Mb The diaphragm 23- engages with the inner side of the longer leg of the U-shaped member 20 as shown, and each of its prongs or forks is perforated at the end and engaged on one of the screws 3I between coil springs 33 and the body I of the instrument. It will readily be seen that spring 40 tends to bias the lever I6 in a clockwise direction around its pivot and against the force exerted by the bel- Qws Extending through holes formed in the inner portions of the arms I0 and II of the body I is a shaft 42. Encircling the end of the shaft 42 which extends beyond the arm I0 is a coiled torsion spring 45, one end of which is attached to the arm I0. and, the other end of which is attachedtothe shaft 42. A portion of the shaft 42 between the arms I0 and II has a flattened surface, as can be seen on Figures 2 and 3. On the opposite; end of the shaft 42 is an operating lever or arm 46 having a knurled portion 41 and a pair of prongs-or fingers 4B and 49 diametrically opposite the'knurled portion 41. The shaft 42 can be-movedagainst theforce of: the torsion spring 45 by the operating lever 46- and is limited in its angular movement in either direction by engagement of thefingers 48 and 49 with a stop member 50. Whenever the shaft 42 is rotated so that the flattened surface, as seen on Figures 2 and 3, is moved to any position except horizontal, the torsion spring tendstoreturn the shaft to its original position. It will be seen from the crossseotion of theshaft 42 that one edge of the flat-- tened surface which is at the central portion of the shaft is slightly-chamfered-or bevelled forming a very small flat surfaceindicated at 53. When the bellows is in itsnormal position having a normal pressure of 15 lbs. therein, as shown in Figure. 2, the arm 21 of bell-crank lever- I5 need not engage the'shaft 42. However, when the bellows 24' is in its extended position, that is when there is apressure of such as 30 lbs. per sq. inch therein as employed in this invention, as. shown in Figure 3-, the arm 21 of the bellcrank lever I5 engages the flat surface of the shaft 42:. It will be seen in Figure 3 that extension. of the. bellows 24 has moved the arms 22 of belle-crank leverl5 to the right, thereby bringing arm 21. intoengagement with shaft 42, and also the lever arm Ifi'and the bimetallic element 2Ihavebeen moved in a counter-clockwise direction about the pivot point of lever arm I6. This described movement of the parts has been brought about by the-forceexerted by the pressure withinlbellows 24' against the opposite force exerted by. the: bellows walls and spring 40. It will be seen in Figure-3 that the upper portion of 'the.leven I6.is engaged-with the screw member 35'which. forms a stop therefor. The assembly formed by the lever- I6, U-shaped member 20 and.bimetallicelement- 2I may now be returned to its. original position by rotation of the shaft 42. in a.counter-clockwisedirection. Rotation of degree, the small flat surface-53 will engage with the arm. 2], asclearly indicated on Figure 4. This-.rotation-of shaft 42 will'be against the force exerted by torsion spring 45' but the force of bellows 24 against the small;flat portion 53 of.

shaft- 42 will cause the shaft 42 to be retained in its position by reason of the friction between the said shaft 42 and arm 21. Release of the pressure within bellows 24, that is, a reduction in the above mentioned pressure from 30 lbs. to 15 lbs., would cause the friction between the shaft 42 and the arm 21 to be reduced sufficiently to permit torsion spring 45 to return shaft 42 to its original position with the relatively large flat side horizontal as seen in Figure 2.

The lower portion of the body I of the instrument carries a rotatable dial 60 having a knurled edge, as shown. The dial 60 has a cam 6| the cam surface of which is of helical conformation. The lower part of the lever I6 is offset to one side of the U-shaped member 20 and is bent over as at 62 so as to engage with the helical edge of the cam 6| when the assembly formed by lever I6, U-shaped member 20 and bimetallic element 2| is in the position shown in Figure 2. Dial 60 has a circular slot 63 through which extends a pointer member 64 to indicate dial readings on the surface of the dial 60, as shown. The pointer member 64 is attached to a vertical support 65 which is attached by a screw 66 to the body I of the instrument. This screw 66 also secures a lug or guide 66a for the dial 60 to the body I of the instrument. It will readily be seen that rotation of the dial 60 in either direction will, by reason of the cam 6|, cause the lever I6 to be moved a small amount in either direction about its pivot.

Obviously, the thermostatic element 2I is moved whenever the lever I6 is moved by rotation of the dial 60. The dial 60 and the cam member 6| provide for adjustment of the instrument when it is t in its normal daytime position, as seen in Figure 2. The lower portion of dial 60 and pointer 64 protrude through a slot in the casing of the instrument so that the adjustments of the daytime temperature can conveniently be made without removing the casing. It will be noted that a screw 61 extends between the legs of the U- shaped member 20 near its bottom portion and provides an additional means for adjusting the instrument by turning the screw and thereby drawing the legs of the U together or forcing them apart. Such adjustment of the screw 01 obviously adjusts the relative position of the thermostatic element 2I. This adjustment is a factory adjustment and cannot be made without removing the casing which normally encloses the instrument.

The upper portion of the body I of the instrument forms a casing I00 of general cylindrical conformation. The casing I00 houses the relay mechanism which, as has been previously explained, forms a part of the instrument and which will be described in detail hereinafter. Numeral II indicates a tube having a bleed port therein such as is ordinarily used in connection with pneumatic control instruments and which extends from casing I00. The bleed port and the control thereof may be referred to as a pilot valve for a large valve forming part of the relay device. Also extending from casing I00 is a support I2 suitably secured to the casing by screws 13 to which is pivoted a vane I4. The vane I4 swings freely about its pivot and at its lower end carries a weight I5 on one side and on the other side engages with the upper end of the bimetallic thermostatic element 2 I. On the side of the vane I4 opposite the weight I5 is a glass bailie plate I6 retained within a suitable casing I1. arranged to engage the conical end of the tube II having the bleed port therein.- Movement of the thermostatic element 2| tending to rotate the vane 14 in a counter-clockwise direction will tend to move the baflle plate 16 away from the bleed port in tube II, thereby increasing the rate of bleed, while movement of the vane 14 in a counterclockwise direction will permit weight 15 to rotate vane I4 for reducing the rate of bleed through tube II.

Figure 5 represents the pneumatic relay or pilot valve device previously referred to which forms the upper part of the control instrument. In practice, the casing enclosing the relay is formed integrally with the body of the control instrument but it is to be understood that the relay may be constructed separately and operatively associated with the other parts of the instrument so as to function in the same manner as when it is formed as an integral part thereof.

The relay comprises generally the casing indicated at I00, the lower part of which may be integrally connected to the body I of the instrument as shown on Figure 5. The casing I00 is made up of sections IOI, I02 and I03, the sections being spaced by diaphragms of the same general circular conformation as the casing sections, all of the elements being rigidly secured together by screws 13. Communicating with the inner end of the opening I06 to which channel 5a connects is a transverse conical opening I 09 in which is screw threaded a plug IIO which forms a needle valve which can be adjusted by means of a screw driver. Plug I I0 is provided with a small longitudinal air passage as shown. The upper part of the opening I09 is sealed by a screw plug II2 leaving a space between the plug II 2 and the needle valve member H0. The needle valve forms a restriction to the supply of air under pressure through pipe 50 and channel 5a, and the air which passes the restriction formed by the needle valve passes through a channel H5. The channel II5 communicates with a similar aligned channel in the sections I02 and I03 and with registering orifices in the diaphragms I04 and I05 which space the sections. The channel II5 connects with a shorter channel H6 in the section I03 of the casing which communicates with the chamber III formed within the section I03 between the diaphragm I05 and the inner wall of the section I03. The tube "II having the bleed port 18 communicates with the chamber III so that air is allowed to bleed from this chamber at a rate as determined by the position of the baffle plate 16 with respect to the bleed port.

Formed in the section IOI of the casing of the relay device is a screw threaded opening for receiving a plug I20. Also formed within the section IOI at the inner end of the plug I20 is an opening I2I which communicates by a passage I22 with the opening I06. Centrally arranged within the plug I 20 is an opening I 25 arranged to receive the stem I26 of a valve member I21, the stem I26 forming a plunger in the opening I25. Around the walls of the opening I25 is formed another opening I28 of annular cross-section which receives a coil spring I29, one end of which engages the inner surface of the plug I20 and the other end of which engages the valve member I2'I. The seat for the valve member I21 is formed by an opening I3I in an internal wall portion I32 of the section v I,0I. The coil spring I29 biases the valve I21 against its seat, as shown.

Within the casing I00 of the pneumatic relay device, a chamber is also formed within the section I02 between the diaphragms I04 and I05.

. Interposed between the two diaphragms'within phragms I04 and I05 will be moved to the right. The valve seat formed by tubular element I40 will thus be moved away from the valve member I21 allowing pressure to be exhausted from chamber I39 through the tubular element I40 into the chamber between the diaphragms and to the atmosphere through port I43. As soon as the forces exerted within chambers I39 and H1 again balance, the tubular element I40 will again seat against the valve member I21 and the system will again be in equilibrium. When the pressure in chamber I39 is reduced by reason of air being exhausted therefrom through the tubular element I40, this reduction in pressure will, of course. be communicated to the valves 09 and 90 and will cause the springs within the bellows operating devices to move the valve in opening direction. From the above, it is readily seen that the valves 83 and 90 are positioned in response to the temperature surrounding the thermostatic element 2I and admit steam at a rate so as to maintain a constant room temperature.

In the evening when it is desired to reset the control instruments of the system so as to maintain a lower temperature during the night, the three-way valve 88 may be reset from the basement or wherever the air compressing apparatus may be located so as to put pipe 81 in communication with the pipe 5. A constant pressure of 30 lbs. per sq. inch will now be communicated to the restrictor I'I0a, to the chamber I2I, and through the branch connection 5b to the bellows 24. As has previously been explained in connection with Figures 1 to 4, this increased pressure within the bellows 24 will reset the control instrument by repositioning the thermostatic element 2|. By reason of its new mounting position, the thermostatic element 2| will operate to maintain a substantially lower temperature at night. This temperature which is to be maintained at night can be adjusted by means of the knurled knob 36 which has already been described in connection with Figures 1 to 4, Obviously, the amount which the lever I6 carrying the thermostatic element is moved to the right, as seen on Figures 1 to 4, is determined by the position of the screw member 35 which forms a stop for the lever I6. The knurled knob 36 is located within the casing of the instrument and adjustment thereof is not intended to be made without removing the casing from the instrument.

With a pressure of 30 lbs. per sq. inch in the header 50, it is readily seen that the pressure beyond the restricting device lIa may at times exceed the original normal value of 15 lbs. per sq. inch at which the supply pressure is maintained during the daytime. For example, when the bleed port is completely closed, a pressure of 30 lbs. per sq. inch will be applied to the diaphragm I05. Inasmuch as the relay mechanism tends to maintain the same pressure within chamber I39 and the valve motors as occurs within chamber II1, the relay device would tend at this time to apply a pressure of 30 lbs. per sq. inch to the valve motors. This is undesirable as this additional pressure may injure the valve motors. In order to prevent this result from occurring, the section I02 of the relay device I00 as seen in Figure 6 is provided with an internal shoulder I4Ia which corresponds to the shoulder I4I' of Figure 5. This shoulder serves as a stop for limiting movement of the diaphragm I to the left. Due to the spring action of the spring member I31, this member must be compressed in order to increase the force applied to the diaphragm I04 by the diaphragm I05. Upon an increase in pressure applied to the diaphragm I 05 this diaphragm will be forced to the left thereby acting through the spring I31 to force the diaphragm I04 to the left which will shift the air valve member I21 from its seat for permitting air under pressure to enter the chamber I39. As described above air will be permitted to enter this chamber until the pressure therein rises sufficiently to force the diaphragm I04 back to its neutral position at which both the air valve and vent valve are closed. While the diaphragm I04 will normally be in its neutral position, this increase in pressure will have caused the dia phragm I05 to assume a position further to the left, this leftward shift of the diaphragm I05 being permitted by the resiliency of the spring member I31. Thus as the pressure in chamber III is increased the diaphragm I05 will assume positions more and more to the left, due to the fact that the spring member I31 must be compressed sufficiently to balance the pressure applied to diaphragm I05. The spring member I31 and the position of the shoulder I4Ia are correlated so that when a pressure of 15 lbs. per sq. inch is applied to the diaphragm I05, the diaphragm will be forced to the left against the action of spring member I31 to just engage the shoulder I4Ia. At this time the spring member I31 must necessarily have been compressed sufficiently to balance the force applied to diaphragm I05 by the air pressure. Inasmuch as this spring member is urging the diaphragm I04 to the left it is necessary that the pressure in chamber I39 be sufficient to maintain the diaphragm I04 in its neutral position and simultaneously provide the necessary reaction for the spring member I31. Thus with the diaphragms I04 and I05 of equal area the pressure maintained in chamber I33 will equal that in chamber H1 or in other words, at this time the pressure in chamber I39 will be 15 lbs. per sq. inch. Due to the fact that the diaphragm I05 is engaging its stop, further increase in pressure on this diaphragm cannot cause it to move any further to the left. The spring member I31 will therefore not be further compressed and consequently the pressure on diaphragm I04 will not have to exceed 15 lbs. per sq. inch in order to maintain this diaphragm in its neutral position at which both the air supply and vent valves are closed.

As has previously been explained in connection with Figures 1 to 4, after the control instrument has been reset as above described to maintain a lower temperature at night, the instrument may be returned to its original daytends through the side wall of the casing enclosing the instrument so that this adjustment of the instrument can be conveniently made by anyone whenever desired. If for any reason,

' the operating lever 46 should be left in the position shown in Figure 4, that is, the instrument having been returned to its daytime setting after having been reset for night temperature, when the pressure within the pneumatic system is & HUMIDITY REUULAHUN.

again reduced from 30 lbs. to lbs. per sq. inch, the operating lever will automatically return to its normal position as seen in Figures 2 and 3.

Figure 7 represents a pneumatic relay device similar to that of Figure 5 but slightly modified in form. Corresponding elements of Figure 7 are correspondingly numbered to those of Figure 5. The diaphragms 204 and 205 of Figure 7 have annular corrugations as distinguished from the diaphragms of Figure 5. Also a third diaphragm member 24! is employed, the peripheral edges of which are retained between the diaphragm 2M and section 202 of the relay device. The internal portion of the diaphragm 2 is offset from its peripheral portions so that it forms a stop for the diaphragm 205 operable in the same manner as the stop formed by the flange Ml of Figure 5. Diaphragm 205 carries a central spring retaining element 244 and between this element and the tubular element 240 is a coil spring 236 which has the same function as the spider type spring I36 of Figure 5. The operation of the device of Figure 7 is the same as that of Figure 5 and has previously been explained in connection with Figures 5 and 6.

From the foregoing, it should be apparent that my improved control instrument avoids certain inherent disadvantages in similar devices heretofore known in that its design automatically prevents undesirable large pressures from being communicated to pneumatically driven valves or damper motors or the like. As is well kunown in the art, these devices are relatively sensitive and must be controlled with considerable precision in order to maintain desired temperatures in buildings being heated or cooled. If pressure beyond that necessary to cause complete closure of these devices is allowed to be communicated to them, the operating mechanism may be given a permanent set or other damaging results to the device may occur. That portion of the structure of the control instrument which provides for returning it to a daytime setting as desired after the control instruments of the system have been reset to a night temperature makes for economical operation of the heating system or the like as a whole inasmuch as an individual room may be maintained at a desired daytime temperature as long as desired after other rooms of a building have become unoccupied without supplying heat to the entire building at a normal daytime rate.

As there are many modifications, variations and changes in the form and application of the invention which will occur to those skilled in the art, it is to be limited only as determined by the appended claims.

I claim as my invention:

1. In a controlling instrument, in combination, a condition responsive element, means actuated by said element, said element being pivotally mounted so that it may move as a lever, resilient means including a pressure responsive mem her for positioning said element, means comprising a lever pivoted so as to engage said pressure responsive member, and operating means for said lever comprising a torsionally biased rock shaft having a flat surface for frictionally engaging said lever, said pressure responsive device acting on said lever to provide a sufiicient degree of frictional engagement between the rock shaft and lever whereby the rock shaft is prevented from being rocked by the torsional bias.

2. In a control instrument, in combination, a condition responsive element, means actuated by Cross Heiezentc aacasco said element, resilient means including a pressure responsive device for positioning said element, a bell-crank lever pivoted so that one arm engages said pressure responsive device, a rock shaft having a flat side adjacent the other arm of said bell-crank lever, said pressure responsive device being operable to move said other arm substantially against said flat side, means comprising a dog for rotating said rock shaft and a torsion spring for resisting rotation of the rock shaft, rotation of the rock shaft being operable to move said bell-crank lever whereby said pressure responsive device is compressed, said rock shaft having a second relatively small fiat surface for frictionally engaging said other arm of the bell-crank lever and retaining the rockshaft in rocked position against the torsion exerted by the torsion spring.

3. In a pneumatic temperature control system, in combination, a branch line connected to a pneumatic motor, a supply line for supplying air to said branch line, valve means for controlling the pressure in said branch line, diaphragm means responsive to the pressure in said branch line for controlling said valve means in a manner to vary the branch line pressure in accordance with a force applied to said diaphragm means, a second diaphragm means, a resilient connection between said first diaphragm means and said second diaphragm means for normally causing said second diaphragm means to apply force to said first diaphragm means in accordance with pressure applied to said second diaphragm means, pilot valve means for controlling the pressure applied to said second diaphragm means from said supply line, a condition responsive element for actuating said pilot valve means, movable mounting means for said condition responsive element, first adjustable stop means for limiting movement of said mounting means in one direction, biasing means for urging said mounting means toward said first stop means, a second stop means for limiting movement of the mounting means in the opposite direction, a pressure motor connected to said supply line for urging said mounting means toward said second stop means, a controller for raising and lowering the pressure in said supply line for causing said mounting means to be urged against either said first or second stop means,

and stop means associated with said second diaphragm means for limiting the force applied by said second diaphragm means to said first diaphragm means through said resilient connection for thereby preventing the branch line pressure from being raised above a predetermined value even though the supply line pressure is raised above such value by said controller.

4. In a pneumatic temperature control system, in combination, a branch line connected to a pneumatic motor, a supply line for supplying air to said branch line, valve means for controlling the pressure in said branch line, diaphragm means responsive to the pressure in said branch line for controlling said valve means in a manner to vary the branch line pressure in accordance with a force applied to said diaphragm means, a second diaphragm means, condition responsive means for varying the pressure applied to said second diaphragm means, a resilient connection between said first and second diaphragm means, stop means for limiting movement of said second diaphragm means, for thereby limiting the force applied to said first diaphragm means by said second diaphragm means through said resilient connection, adjusting means for varying the standard of the condition maintained by said condition responsive means, a pressure motor responsive to supply line pressure for actuating said adjusting means, and means for varying the pressure in said supply line for actuating said pressure motor.

5. In a pneumatic control system, in combination, a source of fluid under pressure, means for selectively changing the pressure of said source between predetermined higher and lower values, a control device adapted to be positioned by variations in the pressure of fluid applied thereto, valve means for controlling the pressure transmitted from said source to said control device, a first diaphragm means responsive to the pressure in said control device for controlling said valve means, a second diaphragm means, condition responsive means for varying the pressure applied to said second diaphragm means between a minimum pressure and the pressure at said source, means for transmitting the force applied to said second diaphragm means to said first diaphragm means, means for limiting the force transmitted from said second diaphragm means to said first diaphragm means to a predetermined value, adjusting means for varying the standard of the condition maintained by said condition responsive means, and a pressure motor responsive to the pressure of said source for actuating said adjusting means.

6. In a pneumatic control system, in combination, a source of fluid under pressure, means for selectively changing the pressure of said source between a lower value and a higher value, a control device adapted to be positioned by variations in the pressure of fiuid applied thereto. valve means adapted to admit selectively pressure from said source to said control device or exhaust said control device, a first diaphragm, a pilot valve adapted to control the pressure transmitted from said source to said first dia phragm, a second diaphragm subject to the pressure in said control device, a resilient connection between said first and second diaphragms, means to prevent movement of said first diaphragm beyond a position corresponding to the lower value of the pressure of the source, a condition responsive device for positioning said pilot valve, and means responsive to the pressure of said source for selecting the value of the condition at which said condition responsive device actuates said pilot valve.

7. In a pneumatic temperature control system, in combination, a branch line connected to a pneumatic motor, a supply line for supplying air to said branch line, valve means for controlling the pressure in said branch line, diaphragm means responsive to the pressure in said branch line for controlling said valve means in a manner to vary the branch line pressure in accordance with a force applied to said diaphragm means, a second diaphragm means, a resilient connection between said first diaphragm means and said second diaphragm means for normally causing said second diaphragm means to apply force to said first diaphragm means in accordance with pressure applied to said second diaphragm means, pilot valve means for controlling the pressure applied to said second diaphragm means from said supply line, a condition responsive element for actuating said pilot valve means, movable mounting means for said condition responsive element, first adjustable stop means for limiting movement of said mounting means in one direction, a second stop means for limiting movement of the mounting means in the opposite direction, a pressure motor connected to said supply line for moving said mounting means between said stop means, a controller for raising and lowering the pressure in said supply line for causing said mounting means to be urged against either said first or second stop means, and stop means associated with said second diaphragm means for limiting the force applied by said second diaphragm means to said first diaphragm means through said resilient connection for thereby preventing the branch line pressure from being raised above a predetermined value even though the supply line pressure is raised above such value by said controller.

8. In a fiuid pressure relay, in combination, a first chamber adapted to be subjected to a variable pressure, a second chamber the pressure in which normally is controlled in accordance with the pressure in said first chamber, a first diaphragm subjected on one side to the pressure within said first chamber, a second diaphragm subjected on one side to the pressure within said second chamber, a mechanical connection between said diaphragms including a resilient portion, pressure inlet and exhaust valves for controlling the pressure in said second chamber and adapted to be opened selectively by said second diaphragm, and stop means for limiting movement of said first diaphragm.

9. In a fluid pressure relay, in combination, a first chamber adapted to be subjected to a variable pressure, a second chamber the pressure in which normally is controlled in accordance with the pressure in said first chamber, a first diaphragm subjected on one side to the pressure within said first chamber and on the opposite side to atmospheric pressure, a second diaphragm subjected on one side to the pressure within said second chamber and on the opposite side to atmospheric pressure, pressure inlet and exhaust valves for controlling the pressure in said second chamber and adapted to be opened selectively by said second diaphragm, connecting means between said first and second diaphragms including a. resilient portion adapted on a rise in pressure within said first chamber to open said inlet valve, and stop means adapted to prevent movement of said first diaphragm beyond a position corresponding to a predetermined relatively high pressure thereby limiting the pressure which will be admitted to said second chamber.

10. In a pneumatic control system, in combination, a source of fluid under pressure, means for selectively changing the pressure of said source between predetermined higher and lower values, a control device adapted to be moved to a first limiting position at a predetermined relatively low pressure of fluid applied thereto and to a second limiting position at a relatively higher pressure substantially equal to the lower pressure available from said source of pressure, valve means for controlling the pressure transmitted from said source to said control device, a first diaphragm means responsive to the pressure in said control device for controlling said valve means, a second diaphragm means, condition responsive means for varying the pressure applied to said second diaphragm means between a minimum pressure and the pressure at said source, means for transmitting the force applied '8 .aasawo to said second diaphragm means to said first dusting means for vowing the (standard of the diaphragm means, means for limiting the force condition maintained by .said oondition respontransmitted from said second diaphragm means sive means, =and -a pressure motor responsive to to said first diaphragm means to a predeterthe pressure of said source for actuating said mined value whereby the pressure admitted to 5 adj ti m a said control device is limited substantially to the PAUL F. 'SHIVERS. lower pressure available [from said source, ad- 

